In a heterogeneous wireless network environment, various wireless networks use different telecommunication technologies. For example, heterogeneous wireless networks may include a global system for mobiles (GSM) network, a wideband code division multiple access (WCDMA) network, and/or a Long Term Evolution (LTE) network,
Each of the WCDMA network and/or GSM network supports both a circuit switched (CS) service and a packet switched (PS) service. However, the LTE network is a wireless communication network which delivers information at a high data transmission rate with low latency, and supports only a packet switched (PS) service. In the LTE network, a CS service (e.g., voice call service) may be provided through a circuit switched (CS) fallback and/or an internet protocol multimedia subsystem (IMS). Herein, the CS fallback may provide CS services such as voice call services, short message services (SMS), location services (LCS), and/or unstructured supplementary service data (USSD) by reuse of the WCDMA and/or GSM networks when user equipment (UE) is served by the LTE network. The CS fallback is available when a LTE service coverage is overlapped with a service coverage of the WCDMA network or the GSM network.
Typically, when UE supporting an LTE technology and a WCDMA/GSM technology redirects from an LTE network to a WCDMA/GSM network, UE may perform a location area update (LAU) or a routing area update (RAU) such as a normal routing area update (normal RAU) or a combined RAU.
However, when a cell change procedure (i.e., inter-radio access technology (Inter-RAT) cell change procedure) due to a cell reselection is performed from the LTE network to the WCDMA/GSM network, a PS domain of the WCDMA/GSM network may have already been barred. In this case, UE may not be able to perform a normal location update procedure. Accordingly, the UE present in the WCDMA/GSM network may not be able to receive paging signals from the WCDMA/GSM network since a position of the UE is not known to the WCDMA/GSM network. Further, the UE holds a temporary identity used in the next update (TIN) value being set to a GUTI value even though the UE is back to the LTE network.
Meanwhile, when an Inter-RAT cell change procedure due to CS fallback is performed from the LTE network to the WCDMA/GSM network, the PS domain of the WCDMA/GSM network may have already been barred. Thereafter, UE may be transferred back to the LTE network by a cell reselection procedure. In this case, the UE typically holds a TIN value being set to a GUTI value, and therefore the UE may not be able to perform a tracking area update (TAU). Therefore, the UE may not be able to receive paging signals from the LTE network.
Accordingly, there is a need to ensure service continuity between such different types of networks in heterogeneous wireless network environment by avoiding a loss of paging signals.